It is desired that an illumination sensor is installed in a display unit that is included in a portable device such as a cellular phone, a smart phone, or a digital camera in order to adjust a light emission amount in accordance with the illumination of external light (ambient light).
It is also desired that a proximity sensor is installed in those portable devices in order to realize lower power consumption so that the display unit is turned off when a face of a user approaches.
In addition, a proximity and illumination sensor in which the illumination sensor and a proximity sensor are integrated has been suggested from a demand for size reduction of those portable devices.
It is strongly demanded that the sensors installed in those portable devices are used to perform detection of the pulse of the user as a new function (application) of those portable devices and a health condition may thereby be confirmed easily.
In related art, as disclosed in PTL 1, a method has been used in which light emitted by a light-emitting diode is received by a photodiode because reflected light that is reflected by a fingertip of a person changes in accordance with the blood flow, the change in the reflected light is detected, and the pulse is thereby detected. This pulse detection requests accurate detection of a signal cycle. Further, PTL 2 discloses pulse detection by using an analog-digital conversion circuit of an integrating type.